Input devices, including touch sensor devices (also commonly called touchpads or proximity sensor devices), as well as fingerprint sensor devices, are widely used in a variety of electronic systems. Touch sensor devices typically include a sensing region, often demarked by a surface, in which the touch sensor device determines the presence, location and/or motion of one or more input objects, typically for purposes of allowing a user to provide user input to interact with the electronic system. Fingerprint sensor devices also typically include a sensing region in which the fingerprint sensor device determines presence, location, motion, and/or features of a fingerprint or partial fingerprint, typically for purposes relating to user authentication or identification of a user.
Touch sensor devices and fingerprint sensor devices may thus be used to provide interfaces for the electronic system. For example, touch sensor devices and fingerprint sensor devices are often used as input devices for larger computing systems (such as opaque touchpads, touch screens and fingerprint readers integrated in or peripheral to notebook or desktop computers). Touch sensor devices and fingerprint sensor devices are also often used in smaller computing systems (such as touch screens and fingerprint readers integrated in mobile devices such as smartphones and tablets).
Touch sensor devices may be used for navigation (NAV) functions. NAV functions may include, for example, detection of the presence of a finger, as well as detecting gestures based on movement of a finger (such as tapping, double-tapping, scrolling, or swiping gestures). It may also be possible to use fingerprint sensor devices for NAV functions, but fingerprint sensor devices typically have a relatively small input sensing region (e.g., less than 10 mm×10 mm), which makes it impossible or impractical to detect fast-motion gestures such as fast swipe gestures through conventional imaging operations. Further, fingerprint sensor devices may have to contend with low signal-to-noise ratio (SNR) issues when disposed under a relatively thick substrate (such as a glass substrate of thickness 300 μm or greater).